Surgeons who perform spinal stabilization procedures using pedicle screw systems typically require a mechanism for manipulating the spinal anatomy prior to tightening or locking the pedicle screw system. Manipulation is commonly performed as a distraction or compression of the vertebral disc space. Vertebral body reduction can also be needed, depending on the condition being treated. Manipulation can be carried out with instrumentation that acts on the pedicle screw.
Surgeons often use polyaxial screws to manipulate the spine. Polyaxial screws, which are defined herein as screws that are rotatable about multiple axes of rotation relative to a receiver body, are often chosen because the polyaxicity of the screws provides maneuverability that allows the stabilization construct to be positionally adjusted in multiple directions. The maneuverability of polyaxial screws can be problematic, however, because the freedom of motion can interfere with attempts to apply compression, distraction or reduction. Monoaxial screws, which are defined herein as screws that are rotatable about one and only one axis of rotation relative to a receiver body, are an alternative that avoids the problems associated with polyaxicity. Nevertheless, there is still a large preference for polyaxial screws. Therefore, there is a need for a pedicle screw assembly that allows for the advantages of polyaxial screws while controlling undesired maneuverability of polyaxial screws.